Radio frequency power amplifiers (RFPAs) are known. Such amplifiers are typically constructed to provide a power output in a range of from a few tenths of a watt to kilowatts and in a frequency range of from a few kilohertz into the megahertz range.
RFPAs, as is known, typical receive an input signal consisting of a modulated RF signal from a signal generation circuit in a base station (external to the RFPA) at a level of from one to several hundred milliwatts magnitude. In its simplest form a RFPA receives the input signal in the milliwatt range and amplifies it to its final value which may then be applied to a transmitting antenna.
In the creation of an RFPA a number of power amplifying devices of varying signal gain characteristics and power handling capabilities may be combined. Overall gain requirements may be obtained by connecting a number of amplifier stages in series, with the overall gain characteristic of the RFPA being equal to the product of the individual stages minus any losses incurred. The use of circuitry splitting the RF signal for application to a plurality of parallel amplifying devices is also often employed to increase the power output capabilites of the RFPA above that available with a single amplifying device. Combining circuitry may then be used to sum the outputs of the individual amplifying stages.
Also present within a RFPA and often combined with amplifying devices is a compensation function. In general a compensation function (or functions) may be defined as being provided by any circuit containing low-pass or high-pass filters, ferrite isolators, temperature or current sensing circuits, output power, and/or reflected power sensing circuits.
The compensation function (or functions) within a RFPA may be accomplished by a variety of methods. One method is through the use of a compensation circuit combined with the amplification circuit. Another way is through the use of splitter and combiner circuits, separate and apart from the amplification circuit. Still further methods include the use of low-pass or high pass filters. Directional couplers may also be used.
Depending on the type of RF amplifying devices, used, one or a combination of the above compensation methods may be used. Amplification and compensation may be combined into a single circuit or may be separated into multiple circuits installed on multiple circuit boards.
Of the RFPAs constructed in the prior art, very little standardization has occurred. In part the reason for the non-standardization relates to RF devices or to the frequency ranges over which an RFPA operates. Each RF device or frequency range, in the past, has tended to generate its own compensation requirements.
In addition, RF power devices of different power levels are typically constructed with a variety of different case configurations and cooling requirements. Differing case configurations often necessitate minor modifications in mounting provisions.
Cooling requirements are typically met through the use of heat sinks and fans where required. The larger the power output of an RF device the larger the heat sink that may be needed. Larger heat sinks, on the other hand, tend to become disproportionately less efficient as output power increases. High power RF devices a few times larger than a smaller unit occasionally require heat sinks many times larger than that of the smaller unit.
Varying RFPA designs in general are inefficient from the standpoint of engineering resource utilization resulting in increased design costs. Varying size and shape, totally apart from amplification considerations, cause hidden costs in accommodating RFPAs in radio systems and assemblies. A need exists for standardization.